Debtor's Knell/Enchantment Questions

Debtor's Knell is an Enchantment. It says "At the beginning of your upkeep, put target creature card in a graveyard into play under your control."
Questions:
If I had two, would the effect be doubled?
Can a creature with Haste attack when it comes in from this ability (I would think so, just not sure)?
When the creature gets put into play, would "Whenever you play a creature spell" apply to said creature?
Thanks for any light you can shed upon this matter.
DWEY

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